1. Field of the Invention
The present invention relates to a semiconductor integrated circuit device including a fuse element.
2. Description of the Related Art
In a semiconductor integrated circuit device manufacturing process there is a method of setting elements for circuit configuration by cutting a fuse element formed of polysilicon, metal, and the like by using, for example, a laser after a wafer manufacturing process is finished. With the use of this method, a resistance value can be corrected to obtain desired characteristics after electrical characteristics of the semiconductor device are measured. The method is thus effective particularly for a semiconductor device that places emphasis on its analog characteristics.
A conventional semiconductor integrated circuit device is illustrated in FIG. 5 and FIG. 6. FIG. 5 is a plan view of fuse elements 103, and FIG. 6 is a sectional view taken along the line A-A? of FIG. 5. As illustrated in FIG. 6, the fuse elements 103 are formed on an element isolation insulating film 102, and are formed of a polycrystalline Si film doped with impurities, which is the same conductive material as that of a gate electrode (not shown) of a MOS transistor.
Further, an opening region 108 that is used for cutting middle portions of the fuse elements 103 with a laser is formed above the fuse elements 103. The opening region 108 is hitherto formed by selectively etching an interlayer insulating film 105 formed for the purpose of metal lamination and a silicon nitride film 106 formed for the purpose of protecting an internal element from moisture coming in from the outside respectively using a mask. At that time, the insulating film on the fuse element 103 should be adjusted to have a thickness in a certain range, taking into consideration variations that occur in a process such as deposition or etching of the insulating film and variations in laser intensity during cutting of the fuse elements 103. The reason is that, if a fuse element 103 is exposed, the fuse element 103 expands under the influence of the moisture and a crack may develop along an interface between the exposed fuse element 103 and a fuse element 103 covered with the insulating film, which may adversely affect the internal element. Meanwhile, when the fuse element 103 is cut with a laser, it is necessary to blow off the insulating film simultaneously with the fuse element 103. At this time, if the insulating film on the fuse element 103 is too thick, the insulating film on the fuse element 103 is not blown off so easily, and thermal energy for the blowing off is transferred to the element isolation insulating film 102 under the fuse element 103 to physically damage the element isolation insulating film 102, which results in generation of a crack. If a residue of the scattered fuse element 103 enters the crack, the residue and a silicon substrate 101 may be electrically connected to each other, leading to abnormal electrical characteristics.
In order to deal with the problem described above, various devices for alleviating damage to a base film have been made that includes measurement and strict control of a film thickness of a fuse opening, increasing the thickness of the insulating film under the fuse element 103 with respect to other element isolating film thicknesses, and laying a damage block material on the base film (for example, Japanese Patent Application Laid-open No. 2010-056557).
However, when the thickness of the insulating film 102 under the fuse element 103 is increased with respect to other element isolating film thicknesses or a material for blocking damage is laid on the base film, there is apprehension that the level difference between the silicon substrate 101 and the element isolation insulating film 102 may be increased. Therefore, the aspect ratio of a contact of an element formed on the silicon substrate 101 becomes very high, and there is a possibility that the contact is not formed or electrical connection is made that exhibits an unusually high contact resistance value. Meanwhile, even if the contact of the element formed on the silicon substrate 101 is electrically connected, a contact to the fuse element 103 may pierce the film of the fuse element 103 to cause a quality abnormality.